This invention relates to a document filing apparatus provided with an ultra high resolution display device using a cathode ray tube.
A document filing apparatus is used for recording and reproducing the information of a document on and from a recording medium. This document filing apparatus has a main unit and a display unit coupled to the main unit through an interface cable. The document is scanned by a document scanner. When the document information obtained from the scanner is transferred to the CRT display device through the interface cable, the document information is displayed on the CRT display device. In this case, the serial signal data corresponding to the document information and also vertical and horizontal synchronizing signals are signal-processed in the main unit and supplied to the CRT display device. Like the conventional television receiver, the CRT display device may have 525 scanning lines, a vertical synrhconizing signal frequency of 60 Hz and a horizontal synchronizing signal frequency of approximately 15.75 kHz. In this case, the upper limit frequency of the serial signal data is 4 to 5 MHz, so that data transfer can be readily effected with an ordinary interface. However, in a display device where an ultra high resolution is required for image display, it is necessary to scan a doeument of an A4 size optically with a scanning density of about 8 lines/mm to obtain ultra high resolution data for display on a cathode-ray tube. In order to obtain display of such high resolution data on the cathode-ray tube directly and without flicker, it is necessary that the apparatus have at least 2,400 effective scanning lines, 1,792 effective horizontal dots and a vertical deflection frequency of 60 Hz. To meet these conditions, a frequency in excess of 100 MHz is required for data. Because such high-frequency data is transferred via an interface cable, it is liable to contain noise components such that it cannot accurately be displayed.